Hybrid Active Damping Control Method for LCL-Filtered Grid-Connected Inverters Using Dual-Current Feedback and Capacitor-Voltage Feedforward Under Weak Grid Conditions

Variations in grid inductance shift the resonance characteristics of LCL filters and can reduce the stability margins of digitally controlled grid-connected inverters. This paper proposes a hybrid active-damping strategy that combines grid-current feedback for current regulation, inverter-current feedback for active damping, and capacitor-voltage feedforward to modify the closed-loop dynamics. An open-loop model incorporating the LCL network, equivalent grid inductance, and digital control delay is derived to evaluate the resonance behavior and small-signal stability of the system. Frequency-domain analysis is performed using a fixed controller parameter set, and comparative simulations are used to assess the contribution of the auxiliary control paths. The strategy is further evaluated through real-time hardware-in-the-loop tests under representative grid-inductance conditions. The frequency-domain results show suppressed resonance-related gain amplification and positive phase margins at all evaluated grid-inductance values. The HIL results show bounded and periodic three-phase grid currents without resonance-induced oscillation. The individual harmonic components from the second to the fortieth order remain below 1% of the fundamental component, and the grid-current total harmonic distortion remains below 1.2% in all evaluated cases. These results show effective resonance damping and consistent grid-current quality under grid-inductance variation.